2-way loudspeakers

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Whenever I think of a 2-way loudspeaker I inevitably refer to them as bookshelves and I am not sure why. There are, of course, many big-box loudspeakers with only two drivers.

I suppose the reason might be that's what you see the most of these days, smaller boxes with but two drivers. But the actual definition of a 2-way loudspeaker has nothing to do with physical size of the box itself. It is as simple as it sounds: the music is divided up in 2-ways, separating the bass notes from the upper notes.

In our continuing discussion on different loudspeaker types I wanted to touch on the idea of separating the duties of the speaker driver between multiple drivers; relative to everything on one full range transducer.

As discussed in earlier posts, the effects of multiple movements on a single driver, moving in and out slowly and quickly at the same time, causes sonic problems to be avoided if possible.

In real life sound - this happens all the time. Take a string on a guitar. When it is plucked it is moving both slowly and quickly at the same time. The difference is, that multiple movement is part of the actual sound it produces. If it didn't do that it wouldn't sound the same. But when we try and reproduce that sound we don't want to repeat the process as that method will add unnaturally to what we hear. So it's a Gordian knot.

One thing we can do is separate the duties of the slow moving driver from the fast moving driver, so the two don't add anything more to what we hear, and let them combine back together as one sound in acoustic space - and that's what happens when we go to a 2-way loudspeaker. We assign the slow moving duties to the woofer and the fast moving properties to a tweeter. This solves one problem, the same driver trying to do both jobs at once, but ushers in a raft on new problems: crossover, difference in actual driver construction, physical separation of the two drivers.

First, the crossover. Its job is to separate the frequencies of sound so the tweeter has only the high notes to reproduce, while the woofer only reproduces the lower notes. This can be as simple as a single capacitor or as complicated as you want. Typically a 2-way crossover has at least two elements, one to limit how high the woofer goes and another to limit how low the tweeter goes.

But problems with crossovers are just the beginning - yet they are perhaps one of the biggest contributors to speaker sound.

Tomorrow let's look at crossovers.

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Paul McGowan

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